All Aero

A number of the Keystone aircraft became one off flying testbeds for various newly developed geared or direct drive versions of the Hornet and Cyclone engines. This programme gave rise to the new designations LB 8, LB 9, LB 10, LB 11, LB 11A and LB-12. Most of these were conversions from existing LB 6 or LB 7 bombers.